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THE PHARMACY
Drug Lesson #4: Diphenhydramine
Mostly known for its brand name Benadryl, the FDA first approved this drug6. Even after 75 years, diphenhydramine is still widely used by health care professionals and is available over the counter for patients to use. In the next installment of my drug lessons, I’ll be discussing the basics of what diphenhydramine is and how it is used in clinical practice.
What is diphenhydramine?
Diphenhydramine belongs to a group of medications called H1 receptor antagonists.¹ The H stands for histamine, an inflammatory chemical in the body that’s released when there is physical damage, infection, or an allergic reaction.
When histamine is released and binds to its receptor, the muscles of the lungs and stomach contract. Additionally, the blood vessels dilate and become more permeable, meaning that white blood cells can easily pass back and forth from the blood vessel to the rest of the body.² histamine also increases gastric acid secretion in the stomach and accelerates the heart rate.
Diphenhydramine binds to the histamine receptor and prevents histamine from binding and exerting its action. All…
